Here is an updated version of LDC patch (V4.1).
In this release, checkpoints finishes quickly if there is a few dirty pages
in the buffer pool following the suggestion from Heikki. Thanks.

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If the last write phase was finished more quickly than the configuration,
the next nap phase is also shorten at the same rate. For example, if we
set checkpoint_write_percent = 50% and the write phase actually finished
in 25% of checkpoint time, the duration of nap time is adjusted to
checkpoint_nap_percent * 25% / 50%.
In the sync phase, we cut down the duration if there is a few files
to fsync. We assume that we have storages that throuput is at least
10 * bgwriter_all_maxpages (this is arguable). For example, when
bgwriter_delay=200ms and bgwriter_all_maxpages=5, we assume that
we can use 2MB/s of flush throughput (10 * 5page * 8kB / 200ms).
If there is 200MB of files to fsync, the duration of sync phase is
cut down to 100sec even if the duration is shorter than
checkpoint_sync_percent * checkpoint_timeout.
I use bgwriter_all_maxpages as something like 'reserved band of storage
for bgwriter' here. If there is a better name for it, please rename it.
Heikki Linnakangas <[EMAIL PROTECTED]> wrote:
> I guess we're fine if we do just avoid excessive waiting per the
> discussion in the next paragraph, and use a reasonable safety margin in
> the default values.
>
> >> Should we try doing something similar for the sync phase? If there's
> >> only 2 small files to fsync, there's no point sleeping for 5 minutes
> >> between them just to use up the checkpoint_sync_percent budget.
> >
> > Hmmm... if we add a new parameter like kernel_write_throughput [kB/s] and
> > clamp the maximum sleeping to size-of-segment / kernel_write_throuput (*1),
> > we can avoid unnecessary sleeping in fsync phase. Do we want to have such
> > a new parameter? I think we have many and many guc variables even now.
>
> How about using the same parameter that controls the minimum write speed
> of the write-phase (the patch used bgwriter_all_maxpages, but I
> suggested renaming it)?
Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center